Fix ICE when lookup method in trait for type that have bound vars

compiler/rustc_typeck/src/check/_match.rs

@@ -31,7 +31,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ => (false, false, false),
         };
 
-        // Type check the descriminant and get its type.
+        // Type check the discriminant and get its type.
         let scrutinee_ty = if force_scrutinee_bool {
             // Here we want to ensure:
             //

compiler/rustc_typeck/src/check/op.rs

@@ -504,7 +504,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 return false;
             }
             // We're emitting a suggestion, so we can just ignore regions
-            let fn_sig = self.tcx.fn_sig(def_id).skip_binder();
+            // FIXME: Instead of exiting early when encountering bound vars in
+            // the function signature, consider keeping the binder here and
+            // propagating it downwards.
+            let fn_sig = if let Some(fn_sig) = self.tcx.fn_sig(def_id).no_bound_vars() {
+                fn_sig
+            } else {
+                return false;
+            };
 
             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
                 if !self.tcx.has_typeck_results(def_id) {

src/test/compile-fail/issue-77910-1.rs

@@ -0,0 +1,11 @@
+fn foo(s: &i32) -> &i32 {
+    let xs;
+    xs
+}
+fn main() {
+    let y;
+    // we shouldn't ice with the bound var here.
+    assert_eq!(foo, y);
+    //~^ ERROR binary operation `==` cannot be applied to type
+    //~| ERROR `for<'r> fn(&'r i32) -> &'r i32 {foo}` doesn't implement `Debug`
+}

src/test/compile-fail/issue-77910-2.rs

@@ -0,0 +1,9 @@
+fn foo(s: &i32) -> &i32 {
+    let xs;
+    xs
+}
+fn main() {
+    let y;
+    if foo == y {}
+    //~^ ERROR binary operation `==` cannot be applied to type
+}